Just going by this info: http://www.radiant-floor-heat.com/site/page/heated-hardwood-floors

That's as much as I know about it.

Took forever to bring the house to temperature, but once there it seemed it wasn't going to get cold for anything.

I used to work in property management and can tell you first hand that turning your ac on and off in the summer is WAY more expensive than if you just turned it on and ran it continuously.

I wonder if this isn't the same case with radiant heating under carpet.

My house is tiny, and I want to beef up the insulation and perhaps add heated flooring as a means to offset the need for oil heat.